The present invention relates to metalloproteases derived from gram positive microorganisms. The present invention provides nucleic acid and amino acid sequences of a metalloproteases identified in Bacillus. The present invention also provides methods for the production of the metalloprotease in host cells as well as the production of heterologous proteins in a host cell having a mutation or deletion of part or all of the metalloprotease of the present invention.
Gram positive microorganisms, such as members of the group Bacillus, have been used for large-scale industrial fermentation due, in part, to their ability to secrete their fermentation products into the culture media. In gram positive bacteria, secreted proteins are exported across a cell membrane and a cell wall, and then are subsequently released into the external media usually maintaining their native conformation.
Various gram positive microorganisms are known to secrete extracellular and/or intracellular proteases at some stage in their life cycles. Some of these proteases are produced in large quantities for industrial purposes. However, a negative aspect of the presence of proteases in gram positive organisms is their contribution to the overall degradation of secreted heterologous or foreign proteins.
The classification of proteases found in microorganisms is based on their catalytic mechanism which results in four groups: serine proteases, metalloproteases, cysteine proteases, and aspartic proteases. These categories can be distinguished by their sensitivity to various inhibitors. For example, serine proteases are inhibited by phenylmethylsulfonylfluoride (PMSF) and diisopropylfluorophosphate (DIFP); metalloproteases by chelating agents; cysteine proteases by iodoacetamide and heavy metals and aspartic proteases by pepstatin. Further, in general, serine proteases have alkaline pH optima, metalloproteases are optimally active around neutrality, and cysteine and aspartic proteases have acidic pH optima (Biotechnology Handbooks, Bacillus. Vol. 2, edited by Harwood, 1989, Plenum Press, New York).
Metalloproteases are the most diverse of the catalytic types of proteases. About half of the families comprise enzymes containing the His-Glu-Xaa-Xaa-His (or HEXXH) motif which has been shown by X-ray crystallography to form part of the site for binding of the metal atom, commonly zinc. In at least one family of metalloproteases, a glutamic acid residue completes the metal-binding site, HEXXH+E. For example, the most well characterized of the metalloproteases, thermolysin, contains this motif. The three dimensional structure of thermolysin shows that, in the HEXXH motif, the His residues are zinc ligands and the Glu residue has a catalytic function. (Methods in Enzymology, Vol. 248, Academic Press, Inc., 1994).
An interesting variation of the HEXXH+E motif can be found in the metalloprotease family, m16, in which this motif is inverted and seen as HXXEH+E. Members of this family include pitrilysin (Methods in Enzymology, Vol. 248, Academic Press, Inc. ,1994, pp. 684-692) and insulinase or insulysin (Methods in Enzymology, Vol. 248, Academic Press, Inc., 1994, pp. 211-215).
The present invention relates to the discovery of a heretofore unknown metalloprotease (MP) found in gram positive microorganisms, uses of the MP in industrial applications, and advantageous strain improvements based on genetically engineering such microorganisms to delete, underexpress or overexpress that MP. The present invention is based upon the discovery that MP has overall amino acid relatedness to Escherichia coli pitrilysin.
The present invention is based upon Applicant""s discovery that the inverted version of the characteristic metalloprotease amino acid motif HXXEH+E and putative transmembrane domains exist in Bacillus subtilis MP. Applicant""s discovery, in addition to providing a new and useful protease and methods of detecting DNA encoding other such proteases in a gram positive microorganism, provides several advantages which may facilitate optimization and/or modification of strains of gram positive microorganisms, such as Bacillus, for expression of desired, e.g. heterologous, proteins. Such optimizations, as described below in detail, allow the construction of strains having decreased proteolytic degradation of desired expression products.
Due to the relatedness of MP to pitrilysin and insulysin, zinc metalloendopeptidases which have been shown to degrade small peptides of less than 7kd such as glucagon and insulin, it can be concluded that MP is also an endopeptidase and would be expected to behave similarly to pitrilysin and insulysin.
The present invention encompasses the naturally occurring MP encoded by nucleic acid found in a Bacillus species as well as the nucleic acid and amino acid molecules having the sequences disclosed in SEQ ID NOS: 1 and 2. In one embodiment, the gram positive microorganism is a Bacillus. In a further embodiment, the Bacillus is preferably selected from the group consisting of Bacillus subtilis, Bacillus stearothermophilus, Bacillus licheniformis and Bacillus amyloliquefaciens. The invention further provides for a metalloprotease that has at least 80%, preferably at least 90%, most preferably 95% homology with the amino acid sequence of SEQ ID NO: 2. The invention also provides for a nucleic acid which encodes a metalloprotease that has at least 80%, preferably at least 90%, most preferably 95% homology with the nucleotide sequence shown in SEQ ID NO:1.
In a preferred embodiment, the present invention encompasses the naturally occurring MP nucleic acid molecule having the sequence found in Bacillus subtilis I-168 strain (Bacillus Genetic Stock Center, accession number 1A1, Columbus, Ohio) in the region of about 1757 kb from the point of origin. In another preferred embodiment, the Bacillus subtilis MP nucleic acid and amino acid molecules have the sequences as shown in FIGS. 1A-1F (SEQ ID NOS:1 and 2).
The present invention provides isolated polynucleotide and amino acid sequences for Bacillus subtilis MP in FIGS. 1A-1F (SEQ ID NOS:1 and 2). Due to the degeneracy of the genetic code, the present invention encompasses any nucleic acid sequence that encodes the Bacillus subtilis MP amino acid sequence. The present invention provides expression vectors and host cells comprising a nucleic acid encoding a gram positive MP. The present invention also provides methods of making the gram positive MP.
The present invention encompasses novel amino acid variations of gram positive MP amino acid sequences disclosed herein that have proteolytic activity. Naturally occurring gram positive MP as well as proteolytically active amino acid variations or derivatives thereof, have application in the textile industry, in cleaning compositions and in animal feed.
The present invention also encompasses amino acid variations or derivatives of gram positive MP that do not have the characteristic proteolytic activity as long as the nucleic acid sequences encoding such variations or derivatives would have sufficient 5xe2x80x2 and 3xe2x80x2 coding regions to be capable of being integrated into a gram positive organism genome. Such variants would have applications in gram positive expression systems where it is desirable to delete, mutate, alter or otherwise incapacitate the naturally occurring metalloprotease in order to diminish or delete its proteolytic activity. Such an expression system would have the advantage of allowing for greater yields of recombinant heterologous proteins or polypeptides.
The present invention provides methods for detecting gram positive microorganism homologues of B. subtilis MP that comprises hybridizing part or all of the nucleic acid encoding B. subtilis MP with nucleic acid derived from gram positive organisms, either of genomic or cDNA origin. Accordingly, the present invention provides a method for detecting a gram positive microorganism MP, comprising the steps of hybridizing gram positive microorganism nucleic acid under low stringency conditions to a probe, wherein the probe comprises part or all of the nucleic acid sequence shown in FIGS. 1A-1F (SEQ ID NO:1); and isolating the gram positive nucleic acid which hybridizes to said probe.
The production of desired heterologous proteins or polypeptides in gram positive microorganisms may be hindered by the presence of one or more proteases which degrade the produced heterologous protein or polypeptide. One advantage of the present invention is that it provides methods and expression systems which can be used to prevent that degradation, thereby enhancing yields of the desired heterologous protein or polypeptide.
Accordingly, the present invention provides a gram positive microorganism that can be used as a host cell having a mutation or deletion of part or all of the gene encoding MP, which results in the inactivation of the MP proteolytic activity, either alone or in combination with mutations in other proteases, such as apr, npr, epr, mpr, bpf or isp, or other proteases known to those of skill in the art. In one embodiment of the present invention, the gram positive microorganism is a member of the genus Bacillus. In a preferred embodiment, the Bacillus is selected from the group consisting of B. subtilis, B. licheniformis, B. lentus, B. brevis, B. stearothermophilus, B. alkalophilus, B. amyloliquefaciens, B. coagulans, B. circulans, B. lautus and B. thuringiensis. In a further preferred embodiment, the Bacillus is Bacillus subtilis. 
In another aspect, the gram positive host cell having one or more metalloprotease deletions or mutations is further genetically engineered to produce a desired protein. In one embodiment of the present invention, the desired protein is heterologous to the gram positive host cell. In another embodiment, the desired protein is homologous to the host cell.
In another embodiment, a host cell is engineered to produce MP. The gram positive microorganism may be normally sporulating or non-sporulating. In a preferred embodiment, the gram positive host cell is a Bacillus. In another embodiment, the Bacillus is selected from the group consisting of B. subtilis, B. licheniformis, B. lentus, B. brevis, B. stearothermophilus, B. alkalophilus, B. amyloliquefaciens, B. coagulans, B. circulans, B. lautus and B. thuringiensis. In a further preferred embodiment, the Bacillus host cell is Bacillus subtilis. 
In a further aspect of the present invention, gram positive MP is produced on an industrial fermentation scale in a microbial host expression system. In another aspect, isolated and purified recombinant MP is used in compositions intended for use in the textile industry, in cleaning compositions, such as detergents, and in animal feeds. Accordingly, the present invention provides a cleaning composition, animal feed and a composition for the treatment of a textile comprising MP. The metalloprotease, MP, may be used alone or in combination with other enzymes and/or mediators or enhancers.
As noted, the present invention provides a cleaning composition comprising a metalloprotease, MP, comprising the amino acid sequence shown in SEQ ID NO:2. Also provided are cleaning compositions comprising a metalloprotease having at least 80%, preferably 90%, more preferably 95% homology with the amino acid sequence shown in SEQ ID NO:2 or comprising a metalloprotease encoded by a gene that hybridizes with the nucleic acid shown in SEQ ID NO:1.
Further there is provided an animal feed comprising a metalloprotease, MP, comprising the amino acid sequence shown in SEQ ID NO:2. Also provided are animal feeds comprising a metalloprotease having at least 80%, preferably 90%, more preferably 95% homology with the amino acid sequence shown in SEQ ID NO:2 or comprising a metalloprotease encoded by a gene that hybridizes with the nucleic acid shown in SEQ ID NO:1.
Also provided is a composition for the treatment of a textile comprising a metalloprotease, MP, comprising the amino acid sequence shown in SEQ ID NO:2. Also provided are compositions for the treatment of a textile comprising a metalloprotease having at least 80%, preferably 90%, more preferably 95% homology with the amino acid sequence shown in SEQ ID NO:2 or comprising a metalloprotease encoded by a gene that hybridizes with the nucleic acid shown in SEQ ID NO:1.